How do I delete preinstalled apps on Android?

You can't completely delete Samsung's built-in apps - the system just won't let you, they're protected. But you can disable pretty much all the unnecessary apps through Settings > Apps, select the one you want and tap "Disable" - they won't run, won't update, and won't take up RAM, though they'll still take up storage space.

It's completely safe, you won't cause any harm to the system. If you need something later, you can always turn it back on the same way.